1. Field of the Invention
The present invention relates to glass compositions, and in particular to W-doped Sn-fluorophosphate glass compositions which can be used to make a fusion-type seal, such as one used to hermetically seal OLEDs (organic light emitting diodes) or other devices where it is important to inhibit/prevent oxygen and moisture penetration.
2. Description of Related Art
In a fusion, or vitreous, type seal, the sealing material must be fused, softened or melted such that it flows and wets the surface to which it is applied. A fusion sealing material may be applied to a single sealing surface, as in glazing or enameling. Alternatively, the sealing material may be employed to join two opposed surfaces. The result is then referred to as an intermediate seal or joint.
The sealing material used to make a fusion-type seal must be heated to a temperature where it becomes soft enough to wet the sealing surface and form a hermetic bond. For many purposes, it is desirable to maintain the sealing temperature as low as possible. This is particularly true when the sealing material is used to seal electrical and electronic articles which commonly employ thermally sensitive parts. Accordingly, considerable attention has been given to glasses which have a low transition temperature (Tg) because this property makes them suitable to be used as sealing material. The transition temperature (Tg) of a glass is the temperature at which the glass is deemed to be transformed from the solid to the liquid state.
U.S. Pat. No. 4,314,031 (Sandford et al.), the contents of which are hereby incorporated herein, discloses low temperature sealing glasses which are known as tin-phosphorus-oxyfluoride glasses. These glasses comprise, in weight percent on an elemental basis, 20-85% Sn, 2-20% P, 3-20% O, 10-36% F and at least 75% total of Sn+P+O+F. In addition, these glasses may contain up to 25% Pb, up to 12% Zr, up to 10% Fe, up to 3% Ti, up to 1% Ca, up to 3% Ba, up to 2% Zn, up to 12% total of Fe+Ti+Ca+Ba+Zn, up to 3% total of Na+K+Li, up to 4% Al, up to 1% Si, and 0-20% total of anion modifiers selected from the group consisting of Cl, Br and I. These glasses have relatively low transition temperatures (Tg) which are frequently in the vicinity of 100° C.
U.S. Pat. No. 5,089,446 (Cornelius et al.), the contents of which are hereby incorporated herein, discloses the addition of Nb in an amount of up to 11% into the tin-phosphorus-oxyfluoride glasses to provide sealing glasses that are capable of forming a fusion seal at a temperature of 350° C. or lower. Although, the glasses disclosed in the '031 patent and the '446 patent work well in many sealing applications there is still a desire to improve upon these special types of low temperature sealing glasses. This is done in the present invention.